Time Travelling Temperatures

Hello from the future. I am a time traveller. You would
think that in the future we have agreed to use a single scale
for measuring temperature. This is not so. In fact, we have all
sorts of scales now. All the big brands have made their own.
This is a bit confusing. Please help me figure it out. In my
day to day work I have to relate to two different scales
$A$ and $B$. Help me find a temperature where
the two scales are the same, so I don’t have to worry about
it.

Input

Input consists of two space-separated integers, $X$ and $Y$. $X$ is the point on $B$ where $A$ is zero. $Y$ is the number of degrees in
$B$ that equal a change of
a single degree in $A$.

Output

Output the temperature where both scales are the same. This
number must have an absolute or relative error of at most
$10^{-6}$. If no such
temperature exists, output “IMPOSSIBLE” (without the quotes)
instead. If more than one such point exists, output “ALL GOOD”
(without the quotes) instead.